On the warmest February day on record in Cambridge, about 60 students at the Massachusetts Institute of Technology opt to stay inside a dimly lit lobby, crunching data and churning out pages of analysis, rather than enjoy the sunny, summer-like Friday afternoon. No, it isn&rsquo;t mid-term time. The students -- handpicked from 400 applicants -- are competing in a datathon hosted by the $26 billion hedge fund Citadel. Ken Griffin&rsquo;s firm is upping the ante in the industry&rsquo;s chase for data scientists and engineers, hosting 18 competitions at universities across the U.S., Britain and Ireland this year. The prize in...